A tokamak bends charged particles into helical paths around magnetic field lines that loop the long way around a torus. The tighter the helix (smaller Larmor radius), the better the particle stays trapped instead of drifting to the wall.
r_L = m·v_⊥ / (q·B) (Larmor radius — orbit radius around a field line)
v ∝ √T (hotter plasma ⇒ faster particles ⇒ wider orbits)
confined when r_L ≪ minor radius of the torus
- Toroidal field — stronger B tightens every particle's helix, the main lever for confinement.
- Plasma temperature — hotter plasma (needed for fusion) means faster particles that are harder to confine — the central engineering trade-off of fusion reactors.
- Particle count — how many test ions are tracked in the visualization.
Real-world relevance: ITER, the international fusion project under construction in France, uses exactly this trade-off — its 5.3 tesla field is engineered to confine plasma heated past 150 million °C long enough for fusion to occur.